Method of making a polycarbonate cross-linked resin

ABSTRACT

Polycarbonate resins containing at least one divalent chain unit of the formula: ##STR1## wherein E represents a trivalent hydrocarbon radical, or a trivalent halogen-substituted hydrocarbon radical, are transitory cross-linkers prepared by thermal degradation of the corresponding acid esters (the ester group being removable under conditions of the degradation by a beta-elimination mechanism). Cross-linked polycarbonate resins exhibit enhanced fire-resistance, especially non-dripping. The cross-linkers are useful to cross-link any resin having a group reactive with a carboxyl group.

This is a division of copending application Ser. No. 281,141, filed Dec.7, 1988, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to polycarbonate resins and more particularlyrelates to branched or cross-linked, fire-resistant polycarbonate resinsand intermediates thereto.

2. Brief Description of the Prior Art

Polycarbonate resins have found wide usage to fabricate a wide varietyof articles such as automotive component parts. Polycarbonate resins ofthe present invention include ones that are cross-linked to enhancetheir properties of fire resistance and particularly the characteristicof "non-dripping" when exposed to high temperatures and open flames. Theterm "non-dripping" as used herein means that when exposed to hightemperatures, particularly open flame, articles molded from the resinsdo not "melt" or liquify so as to form liquid drops (drippings).

A wide variety of copolyester-carbonate resins are also known in theprior art as is the method of their preparation; see for example U.S.Pat. No. 4,487,896.

Copolycarbonates of bisphenol-A and 4,4-bis(4-hydroxyphenyl) alkanoateswere described by Fischer, et al., Journal of Applied Polymer Science,Vol. 10, pp. 245-252 (1966).

The U.S. Pat. No. 3,285,875 to Battenbruch et al. describes thecross-linking or "curing" of polycarbonate resins by atransesterification method, resulting in a molecular weight build-up ofthe resin. The method mandates the use of a transesterificationcatalyst.

SUMMARY OF THE INVENTION

The invention comprises a transitory polycarbonate resin, containing inthe polymer chain at least one divalent moiety of the formula: ##STR2##wherein E is selected from the group consisting of trivalent hydrocarbonradicals containing from 1 to 15 carbon atoms, inclusive, andhalogen-substituted trivalent hydrocarbon radicals containing from 1 to15 carbon atoms, inclusive.

The term "trivalent hydrocarbon radical" as used herein meanshydrocarbyl as defined below, wherein two additional hydrogen atoms havebeen removed.

The transitory resins of the invention are useful as intermediates inthe preparation of branched or cross-linked polycarbonate resins.

The invention also comprises branched or cross-linked polycarbonateresin compositions prepared with the use of the polycarbonate resinshaving chain moieties of the Formula (I). The cross-linkedpolycarbonates of the invention are characterized-in-part by an enhancednon-dripping property when exposed to high temperatures or open flame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The polycarbonate resins of the invention, i.e.; the resins containing aunit of the Formula (I), may be prepared by the thermolytic degradationof corresponding polycarbonate resins having chain units of the formula:##STR3## wherein E is as previously defined and R is a hydrocarbyl groupor a halogen-substituted hydrocarbyl group which is amenable tobeta-elimination upon exposure to heat.

The term "hydrocarbyl" as used herein means the monovalent moietyobtained upon removal of a hydrogen atom from a parent hydrocarbon.Representative of aliphatic hydrocarbyl are alkyl of 1 to 15 carbonatoms, inclusive such as methyl, ethyl, propyl, butyl, pentyl, hexyl,heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl,pentadecyl and isomers thereof; cycloalkyl of 3 to 8 carbon atoms,inclusive, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,cycloheptyl, cyclooctyl; alkyl substituted cycloalkyl of 4 to 15 carbonatoms, inclusive, such as 2-methylcyclopropyl, 3,4-dimethylcyclohexyl;alkenyl of 3 to 15 carbon atoms, inclusive, such as allyl, 3-hexenyl,2,4-pentadienyl; and aralkyl of 7 to 15 carbon atoms, inclusive, such asbenzyl, phenethyl, phenpropyl, phenbutyl, phenoctyl and the like. In theformula (II) given above preferred hydrocarbyl groups have a hydrogenatom on the carbon beta to the oxa atom in the structure of the Formula(II), for example ethyl and isopropyl. Preferably R represents an alkylor a cycloalkyl group amenable to removal by thermal degradation.

The term "halogen" is used herein in its normally accepted sense asembracive of chlorine, bromine, iodine and fluorine.

Thermal degradation of the polycarbobate resins containing units of theFormula (II) given above yield the corresponding polymers having unitsof the Formula (I). The thermal degradation, i.e.; exposure totemperatures of 100° C. to 350° C., preferably 200° C. to 300° C., isfor a period of time sufficient to effect removal of the R group(generally 5 to 60 minutes). Under the conditions of the thermolyticdegradation to remove the R groups, transitory carboxyl groups areformed, i.e.; units of the Formula (I) where the R group is replacedwith a hydrogen atom, creating a cross-linking site (the carboxylgroup-bearing moiety). The active crossing-link site may immediatelyreact to cross-link with an adjacent polycarbonate resin chain. This isbelieved to occur by reaction of the generated free CO₂ H group with acarbonate or ester functional group in a repeat unit of an adjacentresin chain. Preferably, the thermal degradation is carried out in theabsence of a transesterification catalyst.

The polycarbonate resins of the invention having chain units of theFormula (I) as given above may be used in at least two different ways ascross-linkers of known polycarbonate resins. First, when prepared as arelatively small ingredient of a known polycarbonate resin composition,i.e.; when the proportion of polymer units of the Formula (II) isrelatively low in the polymer product of the polymerization, thereoccurs a composition containing both known polycarbonate chains [withoutchain moieties of the formula (II)] and the chains having units of theFormula (II). The latter polymer chains may then be subjected todegradative conditions as previously described for removal of the Rgroup, whereupon cross-linking with the adjacent known resin chains,also present occurs as described above.

In a second manner of use, polycarbonate resin compositions may beprepared having a relatively high content of the chain units of theFormula (II). These compositions may be added in any desired proportionto known and conventional polycarbonate resin compositions as additivecross-linking agent precursors and upon exposure of the resultingmixtures to conditions for removal of the R group as described above,will function as cross-linkers.

The cross-linked polycarbonate resin product compositions of theinvention exhibit improvements in certain physical properties of moldedarticles such as heat resistance, solvent resistance, thermal creepresistance, flame resistance and drip retardancy, compared to theprecursor uncross-linked polycarbonate resins.

The polycarbonate resin cross-linkers and cross-linked resins of theinvention described above may have a weight average molecular weight offrom about 10,000 to about 200,000, preferably from about 30,000 toabout 50,000 and an intrinsic viscosity, as measured in methylenechloride at 25° C., of at least about 0.25 dl/gm, preferably from about0.45 to about 1.40 dl/gm.

The resin compositions containing polymers having chain units of theFormula (II) may also be admixed with various commonly known and usedprocessing additives such as, for example, antioxidants; antistaticagents; inert fillers such as glass, talc, mica, and clay; ultravioletradiation absorbers such as the benzophenones, benzotriazoles, and thelike; hydrolytic stabilizers such as the expoxides disclosed in U.S.Pat. Nos. 3,489,716, 4,138,379 and 3,839,247, all of which areincorporated herein by reference; color stabilizers such as theorganophosphites; thermal stabilizers such as a phosphite; and flameretardants. A wide variety of flame retardancy additives useful inpolycarbonate and copolyester-carbonate resin compositions are known andmay be employed herein. Some particularly useful flame retardants arethe alkali and alkaline earth metal salts of sulfonic acids. These typesof flame retardants are disclosed in U.S. Pat. Nos. 3,775,367;3,933,734; 3,931,100; 3,978,024; 3,948,851; 3,926,980; 3,919,167;3,909,490; 3,953,396; 3,953,300; 3,917,559; 3,951,910 and 3,940,366, allof which are hereby incorporated herein by reference thereto. Uponthermal degradation of these compositions, cross-linked compositions ofthe invention are also obtained.

The term "polycarbonate resin" as used herein means synthetic polymericresins containing recurring chain units of the formula: ##STR4## whereinD is a divalent aromatic radical of the dihydric phenol employed in thepolymerization reaction, which comprises the reaction of the dihydricphenol with a carbonate precursor.

Polycarbonate resins and their method of preparation are well known; seefor example the details provided in the U.S. Pat. Nos. 3,028,365;3,334,154; 3,275,601; 3,915,926; 3,030,331; 3,169,121; 3,027,814; and4,188,314, all of which are incorporated herein by reference thereto.

In general, the method of polymerization comprises the reaction of adihydric phenol with a carbonyl halide (the carbonate precursor).

Although the reaction conditions of the preparative processes may vary,the interfacial polymerization processes typically involve dissolving ordispersing the phenol reactant in a suitable water immiscible solventmedium and contacting the reactants with the carbonate precursor, suchas phosgene, in the presence of a suitable catalyst and an aqueouscaustic solution under controlled pH conditions. The most commonly usedwater immiscible solvents include methylene chloride,1,1-dichloroethane, chlorobenzene, toluene, and the like.

The catalyst employed accelerates the rate of polymerization of thedihydric phenol reactant with the carbonate precursor. Representativecatalysts include but are not limited to tertiary amines such astriethylamine, quaternary phosphonium compounds, quaternary ammoniumcompounds, and the like. The preferred process for preparingpolycarbonate resins of the invention comprises a phosgenation reaction.The temperature at which the phosgenation reaction proceeds may varyfrom below 0° C., to above 100° C. The phosgenation reaction preferablyproceeds at temperatures of from room temperatures (25° C.) to 50° C.Since the reaction is exothermic, the rate of phosgene addition may beused to control the reaction temperature. The amount of phosgenerequired will generally depend upon the amount of the dihydric phenoland the amount of any dicarboxylic acid also present.

Dihydric phenol reactants employed to prepare polycarbonate resins aregenerally well known compounds as are methods of their preparation.Representative of such dihydric phenols are phenolic diols of thegeneral formula: ##STR5## wherein A is selected from the groupconsisting of a divalent hydrocarbon radical containing from 1 to about15 carbon atoms; a halogen-substituted divalent hydrocarbon radicalcontaining from 1 to about 15 carbon atoms and divalent groups such as:##STR6## Each X in the Formula (IV) is independently selected from thegroup consisting of halogen, hydrocarbyl such as an alkyl group of from1 to about 8 carbon atoms; an aryl group of from 6-18 carbon atoms, anaralkyl group of from 7 to about 14 carbon atoms, an oxyalkyl group offrom 1 to about 8 carbon atoms, and an oxyaryl group of from 6 to 19carbon atoms; and wherein m is zero or 1 and y is a whole number integerof from 0 to 4, inclusive.

Typical of some of the dihydric phenols that are advantageously employedare bis-phenols such as bis(4-hydroxyphenyl) methane,2,2-bis(4-hydroxy-3-methylphenyl)propane,4,4-bis(4-hydroxyphenyl)heptane,2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane,2,2-bis(4-hydroxy-3,5-dibromophenyl)propane; dihydric phenyl ethers suchas bis(4-hydroxphenyl)ether, bis(3,5-dichloro-4-hydroxyphenyl)ether;dihydroxybiphenyls such as 3,3'-dichloro-4,4'-dihydroxybiphenyl;dihydroxyaryl sulfones such as bis(4-hydroxyphenyl)sulfone,bis(3,5-dimethyl-4-hydroxyphenyl)sulfone; dihydroxy benzenes, such asresorcinol, hydroquinone, halo- and alkyl-substituted dihydroxy benzenessuch as 1,4- dihydroxy-2,5-dichlorobenzene,1,4-dihydroxy-3-methylbenzene; and dihydroxy diphenyl sulfides andsulfoxides such as bis(4-hydroxyphenyl)-sulfide and bis(4-hydroxyphenyl)sulfoxide. A variety of additional dihydric phenols are also availableand are disclosed in U.S. Pat. Nos. 2,999,835; 3,028,365 and 3,153,008,all of which are incorporated herein by reference. It is, of course,possible to employ two or more different dihydric phenols or acombination of a dihydric phenol with glycol.

Preferred dihydric phenols of Formula (IV) are the 4,4'-bisphenols.

The carbonate precursor employed in the preparation of knownpolycarbonate resins as well as resins having chains including themoieties of Formula (II) may be a carbonyl halide, a diarylcarbonate, ora bishaloformate. The carbonyl halides include carbonyl bromide,carbonyl chloride, and mixtures thereof. The bishaloformates include thebishaloformates of dihydric phenols such as bischloroformates of2,3-bis(4-hydroxyphenyl)propane, hydroquinone, and the like; or thebischloroformates of glycols such as the bischloroformates of ethyleneglycol, neopentylene glycol, polyethylene glycol, and the like. Typicalof diarylcarbonates which may be employed are diphenyl carbonate, andthe di(alkylphenyl)-carbonates such as di(tolyl)carbonate. Some othernon-limiting illustrative examples of suitable diarylcarbonates includedi(napthyl)carbonate, phenyl tolyl carbonate, and the like.

The preferred carbonate precursors are the carbonyl halides, withcarbonyl chloride, also known as phosgene, being the preferred carbonylhalide.

The term "polycarbonate" as used herein is also inclusive ofcopolyester-polycarbonates, i.e.; resins which contain in addition torecurring polycarbonate chain units of Formula (III) given above,repeating or recurring carboxylate units, for example of the formula:##STR7## wherein R² is as defined below.

The copolyester-polycarbonate resins are also prepared by polymerizationtechniques, well known to those skilled in the art; see for example theU.S. Pat. Nos. 3,169,121 and 4,487,896.

In general the copolyester-polycarbonate resins are prepared asdescribed above for the preparation of polycarbonate homopolymers, butby the added presence of a difunctional carboxylic acid (esterprecursor) in the water immiscible solvent.

In general, any difunctional carboxylic acid (dicarboxylic acid)conventionally used in the preparation of linear polyesters may beutilized in the preparation of the copolyester-carbonate resins of theinstant invention. Generally, the difunctional carboxylic acids whichmay be utilized include the aliphatic carboxylic acids, the aromaticcarboxylic acids, and the aliphatic-aromatic carboxylic acids. Theseacids are well known and are disclosed for example in U.S. Pat. No.3,169,121, which is hereby incorporated herein by reference.Representative of such difunctional carboxylic acids are difunctionalcarboxylic acids of the formula: ##STR8## wherein R² is a divalenthydrocarbylene group such as an alkylene, alkylidene, or cycloalkylenegroup; an alkylene, alkylidene or cycloalkylene group containingethylenic unsaturation; an aromatic group such as phenylene,biphenylene, and the like; two or more aromatic groups connected throughnon-aromatic linkages such as alkylene or alkylidene groups; and adivalent aralkyl radical such as tolylene, xylylene, and the like.

Preferred difunctional carboxylic acids employed are the aromaticdicarboxylic acids. Particularly useful aromatic dicarboxylic acids arethose represented by the general formula: ##STR9## wherein j is apositive whole integer having a value of from 0 to 4 inclusive; and eachR³ is independently selected from the group consisting of alkylradicals, preferably lower alkyl radicals (containing from 1 to about 5carbon atoms).

Mixtures of these difunctional carboxylic acids may be employed as wellas single acids. Therefore, where the term difunctional carboxylic acidis used herein it is to be understood that this term includes mixturesof two or more different difunctional carboxylic acids as well asindividual carboxylic acids.

Most preferred as aromatic dicarboxylic acids are isophthalic acid,terephthalic acids, and mixtures thereof. A particularly usefuldifunctional carboxylic acid comprises a mixture of isophthalic acid andterephthalic acid wherein the weight ratio of terephthalic acid toisophthalic acid is in the range of from about 10:1 to about 0.2:9.8.

Rather than utilizing the difunctional carboxylic acid per se, it ispossible, and sometimes even preferred, to employ the reactivederivatives of said acid. Illustrative of these reactive derivatives arethe acid halides. The preferred acid halides are the acid dichloridesand the acid dibromides. Thus, for example, instead of using isophthalicacid, terephthalic acid or mixtures thereof, it is possible to employisophthaloyl dichloride, terephthaloyl dichloride, and mixtures thereof.It should be understood that when the term "difunctional carboxylicacid" is used herein, included are the reactive derivatives.

The proportions of reactants employed to prepare thecopolyester-carbonate resins of the invention will vary in accordancewith the proposed use of the product resin. Those skilled in the art areaware of useful proportions, as described in the U.S. patents referredto above. In general, the amount of the ester bonds may be from about 5to about 90 mole percent, preferably from about 35 to about 80 molepercent, relative to the carbonate bonds. For example, 5 moles ofbisphenol-A reacting completely with 4 moles of isophthaloyl dichlorideand 1 mole of phosgene would give a copolyester-carbonate of 80 molepercent ester bonds.

Also included within the scope of the instant invention are randomlybranched polycarbonate resins wherein a minor amount (typically between0.05 and 2 mole percent, based on the quantity of dihydric phenol used)of a polyfunctional aromatic compound is a co-reactant with the dihydricphenol in the reaction mixture, comprising also the carbonate precursorand optionally the ester precursor; to provide a thermoplastic randomlybranched polycarbonate. These polyfunctional aromatic compounds may behydroxyl, carboxyl, carboxylic anhydride, haloformyl, or mixturesthereof. Some illustrative non-limiting examples of these polyfunctionalcompounds include trimellitic anhydride, trimellitic acid, trimellityltrichloride, 4-chloroformyl phthalic anhydride, pyromellitic acid,pyromellitic dianhydride, mellitic acid, mellitic anhydride, trimesicacid, benzophenonetetracarboxylic acid, benzophenonetetracarboxylic acidanhydride, and the like. Other organic polyfunctional compounds usefulin making randomly branched polycarbonates are disclosed in U.S. Pat.Nos. 3,635,895 and 4,001,184, both of which are incorporated herein byreference.

In the conventional polymerization methods of preparing polycarbonates,a molecular weight regulator (a chain stopper) is generally added to thereaction mixture prior to or during the contacting with a carbonateprecursor. Useful molecular weight regulators include, but are notlimited to, monohydric phenols such as phenol, chroman-I,paratertiarybutylphenol, p-cumylphenol and the like. Techniques for thecontrol of molecular weight are well known in the art and are used forcontrolling the molecular weight of the resins of the present invention.

Polycarbonate resins having polymer chain units of the Formula (II)given above are generally well known and may be prepared by the methoddescribed by Fischer et al., supra. The method comprises, in brief,polymerization of a dihydric phenol ester of the formula: ##STR10##wherein E and R are is as previously defined, with a carbonate precursoras previously described, preferably with the additional presence of adihydric phenol of the Formula (IV) given above.

The polymerization may be carried out employing only dihydric phenolesters of the Formula (VII) given above, or with a mixture of the phenolesters (VII) with dihydric phenols of the Formula (IV) previouslydescribed. Although any proportion of the dihydric phenols (IV) and(VII) may be used, for example, in a mole ratio of from 1 to 99:99-1,there is a preference for a mole ratio of 2 to 50:50 to 98 VII:IV.

The diphenol esters of the Formula (VII) may be prepared by esterifyingthe corresponding acids, i.e.; the diphenols of the Formula (VII)wherein R is hydrogen, with an appropriate alcohol of the formula:

    R--OH                                                      (VIII)

wherein R represents hydrocarbyl or halogen-substituted hydrocarbylamenable to beta-elimination as described above, in the presence of anesterification catalyst such as an organic acid. The esterification isadvantageously carried out in the presence of an inert organic solventfor the reactants and the ester product or a large excess of the alcohol(VIII); see Fischer et al., supra. The ester product is separated fromthe reaction mixture by conventional techniques of extraction, washingand solvent removal. Alternatively, the esters of formula (VII) may beprepared by the method described in British Patent specification952,591.

Alcohols of the Formula (VIII) given above are generally well known andinclude, for example, cyclohexyl alcohol, 4-tert-butyl-cyclohexylalcohol and, preferably, ethyl alcohol, isopropyl alcohol or1-ethylpropyl alcohol. Also useful are the halogen-substitutedhydrocarbon alcohols.

The following examples and preparations describe the manner and processof making and using the invention and set forth the best modecontemplated by the inventor of carrying out the invention but are notto be construed as limiting the invention. Where reported, the followingtests were carried out:

Intrinsic Viscosity (IV)

The intrinsic viscosity was measured at a temperature of 25° C. inmethylene chloride and is reported in deciliters/gram (dl/g).

Glass Transition Temperature (Tg):

The glass transition temperatures were determined by using aPerkin-Elmer DSC-2B instrument which measures the glass transitiontemperature or (Tg) by differential scanning calorimetry.

Degree of Cross-Linking (gel formation); Gel Analysis

Five gram samples of the resin powder were placed in petri dishespre-treated with a silicone-based mold release agent, and the dishesplaced in a 300° C./3mm vacuum oven for either 1/2 or one hour. Only twosamples were heat treated at a time in this manner and they were placedside-by-side in identical positions in the oven in order to avoidpossible variability in test temperature due to non-uniformity oftemperature within the oven.

Two gram samples of each heat treated resin were then allowed to standin 150 ml methylene chloride for 24 hours. Any gels that formed werethen separated from the solution, and the solvent removed to provide asample of the soluble resin for IV analysis. The gels were thenextracted three more times with 150 ml portions of methylene chloride,with the samples being allowed to stand 48 hours, 48 hours and 3 hoursrespectively. After the third and fourth extractions the samples weredried and weighed, and in all cases were found to show no additionalloss in weight on the fourth extraction. The percent of gel is theresidual weight divided by the original weight of the heat-agedmaterial, multiplied by 100.

PREPARATION 1

Isopropyl Diphenolate--In a 3000 ml flask fitted with a Dean-Stark trapwere mixed 572 g (2.0 moles) diphenolic acid, 1500 ml isopropanol and 10g toluene sulfonic acid. The mixture was refluxed for 22 hrs, withgradual removal of 500 ml of condensate (From azeotrope tables, thecondensate should be 12% water). 1000 ml methylene chloride and 1000 mlwater were then mixed with the reaction mixture and the methylenechloride layer then washed with water until washings were pH 5. Dryingover MgSO₄ and removal of solvent yielded 631 g of crystalline solid.Recrystallization from 500 ml ethyl acetate and careful washing with 3X50 ml ethyl acetate yielded 498 g of powder, mp 128°-130.5° C. and nmrindicating the desired compound in good purity. Recrystallization of asample a second time from ethyl acetate did not change the mp.

PREPARATION 2

Ethyl Diphenolate, 572 g (2.0 mole) diphenolic acid was reacted with1000 ml ethanol and 10 g toluene sulfonic acid for 30 hrs with removalof 750 ml of volatiles using the same procedure as described for theisopropyl ester. Work-up and re-crystallization were also the same,yielding 320 g of crystalline product with M.P. of 124°-129° C. and withnmr indicating the desired compound in good purity. Partial removal ofsolvent from the mother liquor yielded about 150 g additional crystals,which was mixed with crude product from other batches andre-crystallized again.

PREPARATION 3

1--Ethypropyl Dipenolate--572 g (2.0 mole) diphenolic acid was reactedwith 220 g (2.5 mole) 3- pentanol and 5 g toluene sulfonic acid in 1000ml toluene for 26 hours using the procedure used for the isopropylester. A water layer separated in the Dean Stark trap and about 37 mlwas collected. After work-up as for the isopropyl ester, solvent wasremoved until volume was 1200 ml. On standing for 3 days, 315 g ofcrystals formed. The crystals were washed with 250 ml of 9/1 mixture oftoluene/ethyl acetate to remove colored impurities, then recrystallizedfrom 300 ml of 7% ethyl acetate in toluene to yield 240 g of slightlypink solid, with M.P. of 130°-135.5° C. and nmr indicating the desiredcompound in good purity.

EXAMPLE 1 (COMPARATIVE EXAMPLE)

This example is not an example of the invention but is made forcomparative purposes.

A 3000 ml four neck flask was fitted with a mechanical stirrer, a pHprobe, an aqueous caustic inlet tube and a Claisen adaptor to which wasattached a dry ice condenser and a gas inlet tube. To the flask wasadded 560 ml water, 680 ml methylene chloride, 2.8 ml triethylamine(0.02 mole), 1.65 g (0.0175 mole, 3.5 mole %) phenol and 114 g (0.50mole) bisphenol-A. With stirring the pH raised to 10 by addition of 25%aqueous sodium hydroxide, then phosgene was introduced into the flask atlg/min for 60 minutes (0.6 mole) with pH maintained at 9.5 to 11.5. ThepH was adjusted to 11 at the end of the reaction. The resin layer wasseparated from the brine layer, washed with 3 weight percent aqueous HCluntil washings remained acidic, then twice with distilled water. Theresin was then precipitated into 3000 ml of methanol in a Warningblender, then washed with additional methanol and dried.

The intrinsic viscosity (IV), glass transition temperature (Tg) andpercent of gels is set forth in Table 1, below.

EXAMPLES 2-7

The procedure of Example 1, supra., is repeated except that a proportion(from 0.01 moles to 0.025 moles) of the bisphenol-A as used therein isreplaced with equal proportions of ethyl diphenolate (Preparation 2,supra), isopropyl diphenolate (Preparation 1, supra) and 1-ethylpropyldiphenolate, (Preparation 3, supra), respectively.

The intrinsic viscosity (IV), glass transition temperature (Tg) andpercent of gels observed for the product resins are set forth in theTable 1, below, with the composition structure.

                                      TABLE 1                                     __________________________________________________________________________                        Initial Resin                                                                 Properties                                                       Ester Resin Composition                                                                    IV  Tg 30 min at 300° C.                                                               60 min at 300° C.                  Example No.                                                                          Mole %                                                                             Structure of R                                                                        dl/g                                                                              °C.                                                                       IV.sup.1                                                                          % gels                                                                             IV.sup.1                                                                          % gels                                __________________________________________________________________________      Control                                                                            0%   --      0.472                                                                             150°                                                                      0.522                                                                              0%  0.540                                                                              0%                                   2.     2%   ethyl   0.471                                                                             147°                                                                      0.541                                                                              0%  0.647                                                                              0%.sup.2                             3.     5%   ethyl   0.421                                                                             143°                                                                      0.833                                                                              0%.sup.2                                                                          0.820                                                                             36%                                   4.     2%   isopropyl                                                                             0.396                                                                             142°                                                                      0.702                                                                             38%  0.316                                                                             69%                                   5.     5%   isopropyl                                                                             0.467                                                                             146°                                                                      0.335                                                                             84%  --.sup.3                                                                          94%                                   6.     2%   1-ethylpropyl                                                                         0.459                                                                             148°                                                                      0.780                                                                             46%  0.425                                                                             73%                                   7.     5%   1-ethylpropyl                                                                         0.460                                                                             144°                                                                      0.349                                                                             85%  --.sup.3                                                                          95%                                   __________________________________________________________________________     .sup.1 IV of soluble portion from extraction of gel                           .sup.2 Trace of gel observed visually, but weight was too low to detect b     the procedure used                                                            .sup.3 Insufficient amount of sample for IV testing                      

EXAMPLE 8

To a reactor fitted with a mechanical agitator are charged 6.0 liters ofdeionized water, 7.0 liters of methylene chloride, 2225 grams (9.8moles) of bisphenol-A, 65.7 g (0.2 mole) isopropyl diphenolate, 14milliliters of triethylamine, 3.4 grams of sodium gluconate, and 32.9grams (0.35 mole) of phenol. Phosgene is introduced at the rate of 36grams/minute and phosgenation is continued for 30 minutes. The pH ismaintained at between 9.5 and 10.5 by the addition of 25% aqueous sodiumhydroxide. After phosgenation has ceased 10 liters of methylene chlorideare added, the brine layer is separated by centrifuge and the resinsolution is washed with aqueous acid and water. The resin is steamprecipitated and dried. The resin has intrinsic viscosity of 0.491.

To this resin is added 0.6 parts by weight per hundred parts by weightof resin of sodium--2,4,5 tricholorobenzene sulfonate and 0.25 parts ofa polycarbonate copolymer of bisphenol-A and tetrabromo bisphenol-Acontaining 30 wt. percent bromine. This resin product is then fed to anextruder operating at a temperature of about 500° F. to extrude theresin into strands and the extruded strands are chopped into pellets.The pellets are then injection molded at about 570° F. into test samplesmeasuring about 5 in×1/2 in×1/16 in. The intrinsic viscosity of themolded test sample is 0.484. The samples are tested for theirflammability characteristics using the procedures described in theUnderwriters Laboratory Bulletin 94 publication. The results are givenin Table 2.

EXAMPLE 9

The procedure of example 8 is used, except 2157 g (0.95 mole)bisphenol-A and 164 g (0.5 mole) of isopropyl diphenolate are used. Theresin has intrinsic viscosity of 0.490. The resin is blended withadditives and molded into parts as for Example 8.

The molded parts have intrinsic viscosity of 0.485. The result of UL 94flammability testing of the sample is given in Table 2.

EXAMPLE 10 (COMPARATIVE EXAMPLE)

Standard polycarbonate resin (Lexan® 140) is prepared from bisphenol-Aby substantially the procedure of Example 8 and blended with additivesand molded into parts as for Example 8. The molded parts have intrinsicviscosity of 0.475. The results of UL 94 flammability testing of thesample is given in Table 2.

                  TABLE 2                                                         ______________________________________                                        Ester Resin                                                                   Composition                                                                             Structure                                                                            Flammability Testing Results                                 Mole %       of R    Rating.sup.1                                                                          Comments                                         ______________________________________                                        Exam- 2%        isopropyl                                                                              V0    no bars dripped flaming                        ple 8                          resin; all bars curled and                                                    contracted in the flame                        Exam- 5%        isopropyl                                                                              V0    no bars dripped flaming                        ple 9                          resin; all bars curled and                                                    contracted in the flame                        Exam- None      --       V2    two out of five bars                           ple 10                                                                              compar-                  dripped flaming resins;                              ative                    all bars elongated in                                example                  the flame                                      ______________________________________                                         .sup.1 Rating in Underwriters Laboratory Bulletin 94 testing on 1/16 inch     thick test samples. Five samples were tested for each example.           

The polycarbonate resins of the invention containing the units of theFormula (I) given above may also be used in the preparation of blockcopolymers, with a wide variety of thermoplastic polymers (for examplepolyamides, polyester, polyurethanes, polyethers and the like). Thus,the polycarbonate resins containing units of the Formula (II) may beblended with a second thermoplastic polymer, as described above. Theterm "blend" as used herein is meant to define a physical combination oftwo or more materials which may additionally involve chemical reactionbetween the two materials. The particular thermoplastic polymer to beblended with the polymer (II) will of course depend on the end use ofthe blended product. Upon thermal degradation as described above,polymers containing units of the Formula (I) are generated and effectthe desired cross-linking.

What is claimed is:
 1. A method of cross-linking a resin having sitesreactive with a carboxylic group, which comprises;adding to the resin apolycarbonate resin, containing in the polymer chain at least onedivalent moiety of the formula; ##STR11## wherein E is selected from thegroup consisting of a trivalent hydrocarbon radical containing from 1 to15 carbon atoms, inclusive, and a halogen-substituted hydrocarbonradical containing from 1 to 15 carbon atoms, inclusive.
 2. The methodof claim 1 wherein the addition is in-situ by first adding to the resinto be cross-linked a polycarbonate resin containing at least one chainmoiety of the formula: ##STR12## wherein E is selected from the groupconsisting of a trivalent hydrocarbon radical containing from 1 to 15carbon atoms, inclusive, and a halogen-substituted hydrocarbon radicalcontaining from 1 to 15 carbon atoms, inclusive, and R is selected fromthe group consisting of hydrocarbyl and halogen-substituted hydrocarbylamenable to beta-elimination upon thermal degradation; andheating theadmixture to a temperature sufficient to cause beta-elimination of the Rgroup.
 3. The method of claim 2 wherein E represents

    CH.sub.3 --C--(CH.sub.2).sub.2


4. The method of claim 3 wherein R is alkyl or cycloalkyl.
 5. The methodof claim 4 wherein R is ethyl.
 6. The method of claim 4 wherein R isisopropyl.
 7. The method of claim 4 wherein R is 1-ethylpropyl.
 8. Themethod of claim 3 wherein the resin to be cross-linked is apolycarbonate resin.
 9. The method of claim 3 wherein the resin to becross-linked is a polyamide resin.
 10. The method of claim 3 wherein thethermal degradation is carried out in the absence of atransesterification catalyst.